The generally accepted means for mounting a catalytic substrate material in a catalytic converter housing is with an intumescent mat material. Mat materials range significantly in weight and thickness per given area. Thin materials are relatively easy to wrap around a substrate. As trends are toward thicker total mat thickness however (i.e. higher mat density in a finished catalytic converter), the process of wrapping the substrate is increasingly more difficult. The difficulty is occasioned by the natural buckling at the inside radius of a thicker material caused by tension in the outside radius. The tension is because the outside surface must travel a circumferentially longer distance than the inside surface of the mat.
One previously known way to reduce the difficulty in a thick mat is to cut the material part way through at various locations around a catalyst substrate to remove tension in the outer circumferential material of the mat. While this process of cutting the outer fibers works well, it is only advantageous if the desired thickness of mat can be obtained from a single layer of material.
Another prior art method for easing the difficulty of wrapping thicker mats is to use multiple thin layers instead. While clearly this method avoids the buckling of thicker mats making wrapping easier, each mat needed to be wrapped separately increasing the number of steps in the process to produce a catalytic converter. More steps generally translate to more cost and more time. For these reasons the method is not desirable.
An attempt to streamline the latter method was to glue the multiple individual thin sheets together at one end or in the center so that they can be applied in a single step. While effective in ordinary multiple wrapping steps, the gluing itself requires additional time and process steps as well as increasing materials cost.
The wrapping of catalytic substrate materials is further complicated by prior art procedures concerned with the mating end edges of the mat. More specifically, prior art joints in the mat have employed a tongue and groove arrangement (see FIG. 1). While the tongue and groove joint is effective for its intended purpose it renders automation of the wrapping process difficult.
Attempts to render the joint more friendly to automation include using an "L" joint (see FIG. 2). While the joint is easier to index, a wrapping process using the joint is still difficult to automate.